1. Field of the Invention
Broadly, the field is external heat engines, which can also be redesigned and used as heat pumps. Within this category die field is external heat engines or heat pumps comprising what might be described as a part of a centrifugal fan acting as a compressor and a second centrifugal fan operated backwards and acting as an expander. When I Say fan I am actually talking about a compressor or an expander. The fan part may differ from conventional centrifugal fans, because the output may be directed with a substantial axial component directed toward the other fan, as opposed to almost entirely tangential output for a standard centrifugal fan. The engine fans also differ from conventional fans in that when the engine is idling, the output of either fan may be zero. In some embodiments, there is an unstable equilibrium when the fluid is merely rotating with the engine as a whole. The engine power output is associated with the circulation of the working fluid relative to the rotating engine. The best versions of the engine are rotating. The circulation produces velocity changes producing pressure and temperature changes due to that circulation and rotation. The rotation of the engine amplifies the effects of the circulation. One embodiment of the invention could be looked at as two substantially centrifugal compressors connected so that the conventional input of one is connected to the conventional input of the other and the conventional output of one is connected to the conventional output of the other. Thus during operation the flow in one compressor is in the reverse of the conventional direction: whereas the flow in the other compressor is in the conventional direction. A substantially centrifugal compressor is a compressor having a rotor or impeller. It may also contain elements of radial compressors. It may also contain other elements, such as flow expanders.
2. Description of Related Art
There are many external heat engines that expand and contract a working fluid. One of my favorites is the Stirling engine which uses a large piston to oscillate the fluid between being cooled and being heated. The oscillation of temperature is caused by sending it through a regenerator and having a heat source on one side and a cooling source on the other side of the regenerator. The power output piston is synchronized out of phase with the oscillator piston. There is friction and pressure loss at both pistons. My invention requires no piston and no chamber that changes volume. Also a regenerator, which causes power loss, is not necessary.
Other engines use a compressor followed by an expander, but then open to the atmosphere. The closest to my invention use centrifugal compressors, similar to axial compressors that push the fluid along the rotation axis of an impeller. A jet engine for example is an internal combustion engine that can use a compressor up front. The impeller moves with respect to its housing. This produces energy loss even when the engine is only idling. It also may produce loss of the working fluid depending on how the impeller shaft is introduced. It may also cause problems when the blades move faster than the speed of sound with respect to the casing in which they reside.
My invention, in its preferred form has essentially no working fluid loss. It also has essentially no energy loss when idling, since there are no parts moving with respect to each other, except at the rotating axle outside the fluid containers. Even the working fluid is almost not moving with respect to its container. Even when the engine is going at full speed, the only sound speed problems would be between the rotating casing and a surrounding container. When idling my engine acts like the child's toy, a rotating top. Also the engine has no moving seals contacting the working fluid, thus requiring no lubrication. The engine has no seals at all, except for lubrication on the axle of the engine. It should last nearly forever with no maintenance.
The most closely related art would be centrifugal compressors, since my invention combines two of these, but the output of each is not tangential and the output of one is at the fan area closest to the axis of rotation. Thus an expansion fan is operated like a compressor in reverse, receiving input far from the axis and expelling output very near the axis. To get a larger difference in pressure between the input and output of the compression fan, the spiral as it goes from the center to the outside can be retrograde (counter to the rotation direction). If retrograde, the normal to the surface that pushes the working fluid has a positive radial component. The larger the pressure ratio, the larger the temperature ratio can be and thus the larger the theoretical efficiency of the engine. The current limits of die compression ratio on centrifugal compressors is about ten to one, when pushing air. External heat will be added after the compression, when the fluid is substantially furthest from the axis of rotation.
Actually the engine does not use a purely centrifugal fan, because after the working fluid almost reaches the extreme distance from the rotation axis, for best efficiency, it must be expelled more nearly parallel to the rotation axis, so it can be directed to the second centrifugal fan, which will act as an expander producing power. The impellers may be partially twisted to accomplish the expulsion of the working fluid in a direction nearly parallel to the rotation axis. Also the fan compartment may be shaped so that the fluid first is traveling away from the other fan but at the time to exit the fan it is traveling more toward the other fan. Thus the fan is a cross between a radial fan and an axial fan and the fan compartment is warped to be more like the curved surface of a half of a sliced bagel. Also each impeller may spiral further from the axis on the side closer to the other fan than on the side further from the other fan, thus allowing a radial component in the velocity as it leaves the fan. Of course there is a large tangential component in inertial space, but not relative to the working fluid container. In a conventional centrifugal fan the output fluid is usually expelled perpendicular to the rotation axis.
The heat cycle of the preferred engine of this invention is as follows. The working fluid goes through adiabatic compression, followed by adding heat far from the rotation axis causing some expansion, followed by adiabatic expansion in a reverse compressor, followed by cooling close to the rotation axis causing some contraction, then repeat often. Ideally, the compression and expansion parts of the cycle are performed adiabatically (no heat added or subtracted from the working fluid). Actually some heat exchange with the chamber may take effect. According to formulas for adiabatic compression, the temperature ratio for a monatomic gas is closer to the pressure ratio than it is for a gas consisting of multiple atoms per molecule. The multiple atoms supply more degrees of freedom and thus more capacity to store the heat caused by the compression. This higher temperature ratio is important for engine efficiency.
Ideally the blades of the centrifugal fans meet the fluid so that the fluid is traveling in a direction parallel to the blade surface just before contact and just after leaving each blade. Each blade may be replaced by several blades at varying distances from the axis. Ideally, for maximum efficiency the pressure difference in each fan is maximized producing the largest temperature ratio possible. The extreme pressure ratio on centrifugal compressors for air is currently about 10:1. At ratios above ten for air the compressor may wear out fast and may be dangerous. There is less problem with a heavier gas such as argon or krypton. A ratio of 5:1 would be adequate for very good efficiency and reduced risk and reduced energy loss within the engine. Other reasons to reduce the pressure ratio will be discussed later.
Of course, the compressor and expander can be made similar to modern compressors in that the fluid in the compressor can be centrifuged by a central rotator and rammed into a set of stationary channels to increase pressure. The fluid would then be sent into the stationary channels for the expander. However, this would dramatically increase flow pressure losses because of high velocity in the stationary parts of the compressor and expander. It would also increase losses due to swirl of the fluid, since fluid angular momentum is increased in the early stage of the compressor and later brought to almost zero in the second stage of the compressor. The fluid angular momentum has to then be brought up again before the fluid is introduced to the outer part of the expander. It is better to rotate the paths from compressor to expander and expander to compressor as is done in my preferred embodiment.
One object of the current invention was to produce an engine/heat pump which, when operating at a steady speed, has no changes in temperature at any particular point. Thus heat loss due to changing operating temperatures at a particular position are negligible. Heat loss due to conduction along the parts with spatial temperature differences can be minimized in several obvious ways.
Another object was to produce an engine where there is essentially no loss of pressure around pistons or blades. Prior engines would produce localized circulations and turbulence especially where the blades are close to the blade casing. There is rapid relative motion between closely spaced components in most if not all prior art In my invention the casing which is touched by the working fluid moves with the same rotation rate as the blades, so the blades do not move with respect to the casing, except for angle adjustments.
Another object of the current invention is to produce an engine comprising a centrifugal compressor and a reverse operated compressor in which the working fluid speeds above Mach 1.3 in the compressor are not a problem, because that speed is actually only relative to the outside of the engine. The speed of the working fluid relative to the blades and to the casing used to contain the working fluid is much smaller. The only high relative speeds are between a substantially stationary container outside the rotating parts and the working fluid container together with any container that may be rotating with the engine, maybe to contain a heat supply for heat exchange maybe using a flow of carbon dioxide and nitrogen if a hydrocarbon is burned. The fluid, probably air if present between the rotating and stationary surfaces, will be near atmospheric pressure or below. Also it will be heated and thus the speed of sound is higher in this fluid. In some solar applications, heat of solar radiation is applied directly to the working fluid container and no fluid heat source is necessary. Thus heat would be exchanged between the working fluid and the surface heated by the sunlight, thus heating the working fluid as it travels from compressor to expander far from the rotation axis. A glass container might be used to prevent heat loss to the atmosphere and also to allow evacuation of air surrounding the engine.
Another object is to produce an engine wherein the working fluid can foe at a much higher pressure internally, where the relative motion with respect to the container is small, and wherein the relative motion of the container with respect to the atmosphere can be much larger.
Another object of the invention was to produce an engine with negligible friction loss, since there are no solid parts moving relative to each other due to the engine cycle. Of course, as with most engines, the output shaft is rotating with respect to parts of the device propelled by the engine.
Another object of the invention was to produce an engine that would have no loss of working fluid to the outside or around pistons, since substantially the working fluid is in a container that does not necessarily change shape or volume, except for stress or strain. Argon and krypton gas would not permeate or escape from its enclosure if steel is Used.
Another object of the current invention was to produce an engine which produces very little metal fatigue, since in the rotating system the rotating parts do not move relative to each other during operation and they maintain a nearly constant rotational speed thus keeping stress almost constant.
Another object of the current invention is to produce an engine that loses very little energy while idling at high speed, because the working fluid can be pumping very slowly.
Another object of the current invention is to produce an engine that needs no lubrication, except at the axle. There is no friction wear in the engine.
Another object of the current invention is to produce an engine that needs no seals. The seals could produce a problem in other engines at high temperature.
Another object of the current invention was to produce a very low loss heat pump that allows the temperature ratio to be varied, by varying the rotation speed.
Another object was to produce a heat pump that can be made from aluminum and use argon as the working fluid.